Re: [Libguestfs] [libnbd PATCH v4 08/11] generator: Add `modifies_fd` flag to the [call] structure

On 8/2/2023 6:39 PM, Richard W.M. Jones wrote: >On Wed, Aug 02, 2023 at 12:40:53PM +0000, Tage Johansson wrote: >>Add a flag (`modifies_fd`) to the [call] structure in generator/API.ml >>which is set to [true] if the handle call may do something with the >>file descriptor. That is, it is [true] for all calls which are or may >>call [aio_notify_*], including all synchronous commands like >>[nbd_connect] or [nbd_opt_go]. >> >>The motivation for this is that the asynchronous handle in the Rust >>bindings uses its own loop for polling, modifying the file descriptor >>outside of this loop may cause unexpected behaviour. Including that the >>handle may hang. All commands which set this flag to [true] will be >>excluded from that handle. The asynchronous (`aio_*`) functions will be >>used instead. >Isn't this just saying that the call is synchronous? > >Rich. Kind of, it is true for all synchronous commands and the functions aio_notify_read() and aio_notify_write(). I could mention those explicitly though and rename the flag to something like "is_synchronous", if you want?

Best regards, Tage >>--- >> generator/API.ml | 32 ++++++++++++++++++++++++++++++++ >> generator/API.mli | 7 +++++++ >> 2 files changed, 39 insertions(+) >> >>diff --git a/generator/API.ml b/generator/API.ml >>index 42b9eec..6e1670d 100644 >>--- a/generator/API.ml >>+++ b/generator/API.ml >>@@ -33,6 +33,7 @@ type call = { >> is_locked : bool; >> may_set_error : bool; >> async_kind : async_kind option; >>+ modifies_fd: bool; >> mutable first_version : int * int; >> } >> and arg = >>@@ -274,6 +275,7 @@ let default_call = { args = []; optargs = []; ret = RErr; >> permitted_states = []; >> is_locked = true; may_set_error = true; >> async_kind = None; >>+ modifies_fd = false; >> first_version = (0, 0) } >> (* Calls. >>@@ -1181,6 +1183,7 @@ Return true if option negotiation mode was enabled on this handle."; >> default_call with >> args = []; ret = RErr; >> permitted_states = [ Negotiating ]; >>+ modifies_fd = true; >> shortdesc = "end negotiation and move on to using an export"; >> longdesc = "\ >> Request that the server finish negotiation and move on to serving the >>@@ -1208,6 +1211,7 @@ although older servers will instead have killed the connection."; >> default_call with >> args = []; ret = RErr; >> permitted_states = [ Negotiating ]; >>+ modifies_fd = true; >> shortdesc = "end negotiation and close the connection"; >> longdesc = "\ >> Request that the server finish negotiation, gracefully if possible, then >>@@ -1221,6 +1225,7 @@ enabled option mode."; >> default_call with >> args = []; ret = RBool; >> permitted_states = [ Negotiating ]; >>+ modifies_fd = true; >> shortdesc = "request the server to initiate TLS"; >> longdesc = "\ >> Request that the server initiate a secure TLS connection, by >>@@ -1259,6 +1264,7 @@ established, as reported by L<nbd_get_tls_negotiated(3)>."; >> default_call with >> args = []; ret = RBool; >> permitted_states = [ Negotiating ]; >>+ modifies_fd = true; >> shortdesc = "request the server to enable structured replies"; >> longdesc = "\ >> Request that the server use structured replies, by sending >>@@ -1285,6 +1291,7 @@ later calls to this function return false."; >> default_call with >> args = [ Closure list_closure ]; ret = RInt; >> permitted_states = [ Negotiating ]; >>+ modifies_fd = true; >> shortdesc = "request the server to list all exports during negotiation"; >> longdesc = "\ >> Request that the server list all exports that it supports. This can >>@@ -1326,6 +1333,7 @@ description is set with I<-D>."; >> default_call with >> args = []; ret = RErr; >> permitted_states = [ Negotiating ]; >>+ modifies_fd = true; >> shortdesc = "request the server for information about an export"; >> longdesc = "\ >> Request that the server supply information about the export name >>@@ -1357,6 +1365,7 @@ corresponding L<nbd_opt_go(3)> would succeed."; >> default_call with >> args = [ Closure context_closure ]; ret = RInt; >> permitted_states = [ Negotiating ]; >>+ modifies_fd = true; >> shortdesc = "list available meta contexts, using implicit query list"; >> longdesc = "\ >> Request that the server list available meta contexts associated with >>@@ -1412,6 +1421,7 @@ a server may send a lengthy list."; >> default_call with >> args = [ StringList "queries"; Closure context_closure ]; ret = RInt; >> permitted_states = [ Negotiating ]; >>+ modifies_fd = true; >> shortdesc = "list available meta contexts, using explicit query list"; >> longdesc = "\ >> Request that the server list available meta contexts associated with >>@@ -1462,6 +1472,7 @@ a server may send a lengthy list."; >> default_call with >> args = [ Closure context_closure ]; ret = RInt; >> permitted_states = [ Negotiating ]; >>+ modifies_fd = true; >> shortdesc = "select specific meta contexts, using implicit query list"; >> longdesc = "\ >> Request that the server supply all recognized meta contexts >>@@ -1521,6 +1532,7 @@ no contexts are reported, or may fail but have a non-empty list."; >> default_call with >> args = [ StringList "queries"; Closure context_closure ]; ret = RInt; >> permitted_states = [ Negotiating ]; >>+ modifies_fd = true; >> shortdesc = "select specific meta contexts, using explicit query list"; >> longdesc = "\ >> Request that the server supply all recognized meta contexts >>@@ -1750,6 +1762,7 @@ parameter in NBD URIs is allowed."; >> default_call with >> args = [ String "uri" ]; ret = RErr; >> permitted_states = [ Created ]; >>+ modifies_fd = true; >> shortdesc = "connect to NBD URI"; >> longdesc = "\ >> Connect (synchronously) to an NBD server and export by specifying >>@@ -1928,6 +1941,7 @@ See L<nbd_get_uri(3)>."; >> default_call with >> args = [ Path "unixsocket" ]; ret = RErr; >> permitted_states = [ Created ]; >>+ modifies_fd = true; >> shortdesc = "connect to NBD server over a Unix domain socket"; >> longdesc = "\ >> Connect (synchronously) over the named Unix domain socket (C<unixsocket>) >>@@ -1941,6 +1955,7 @@ to an NBD server running on the same machine. >> default_call with >> args = [ UInt32 "cid"; UInt32 "port" ]; ret = RErr; >> permitted_states = [ Created ]; >>+ modifies_fd = true; >> shortdesc = "connect to NBD server over AF_VSOCK protocol"; >> longdesc = "\ >> Connect (synchronously) over the C<AF_VSOCK> protocol from a >>@@ -1961,6 +1976,7 @@ built on a system with vsock support, see L<nbd_supports_vsock(3)>. >> default_call with >> args = [ String "hostname"; String "port" ]; ret = RErr; >> permitted_states = [ Created ]; >>+ modifies_fd = true; >> shortdesc = "connect to NBD server over a TCP port"; >> longdesc = "\ >> Connect (synchronously) to the NBD server listening on >>@@ -1975,6 +1991,7 @@ such as C<\"10809\">. >> default_call with >> args = [ Fd "sock" ]; ret = RErr; >> permitted_states = [ Created ]; >>+ modifies_fd = true; >> shortdesc = "connect directly to a connected socket"; >> longdesc = "\ >> Pass a connected socket C<sock> through which libnbd will talk >>@@ -1996,6 +2013,7 @@ handle is closed. The caller must not use the socket in any way. >> default_call with >> args = [ StringList "argv" ]; ret = RErr; >> permitted_states = [ Created ]; >>+ modifies_fd = true; >> shortdesc = "connect to NBD server command"; >> longdesc = "\ >> Run the command as a subprocess and connect to it over >>@@ -2031,6 +2049,7 @@ is killed. >> default_call with >> args = [ StringList "argv" ]; ret = RErr; >> permitted_states = [ Created ]; >>+ modifies_fd = true; >> shortdesc = "connect using systemd socket activation"; >> longdesc = "\ >> Run the command as a subprocess and connect to it using >>@@ -2404,6 +2423,7 @@ requests sizes. >> optargs = [ OFlags ("flags", cmd_flags, Some []) ]; >> ret = RErr; >> permitted_states = [ Connected ]; >>+ modifies_fd = true; >> shortdesc = "read from the NBD server"; >> longdesc = "\ >> Issue a read command to the NBD server for the range starting >>@@ -2443,6 +2463,7 @@ on failure." >> optargs = [ OFlags ("flags", cmd_flags, Some ["DF"]) ]; >> ret = RErr; >> permitted_states = [ Connected ]; >>+ modifies_fd = true; >> shortdesc = "read from the NBD server"; >> longdesc = "\ >> Issue a read command to the NBD server for the range starting >>@@ -2535,6 +2556,7 @@ on failure." >> optargs = [ OFlags ("flags", cmd_flags, Some ["FUA"]) ]; >> ret = RErr; >> permitted_states = [ Connected ]; >>+ modifies_fd = true; >> shortdesc = "write to the NBD server"; >> longdesc = "\ >> Issue a write command to the NBD server, writing the data in >>@@ -2568,6 +2590,7 @@ L<nbd_can_fua(3)>)." >> args = []; optargs = [ OFlags ("flags", shutdown_flags, None) ]; >> ret = RErr; >> permitted_states = [ Connected ]; >>+ modifies_fd = true; >> shortdesc = "disconnect from the NBD server"; >> longdesc = "\ >> Issue the disconnect command to the NBD server. This is >>@@ -2605,6 +2628,7 @@ A future version of the library may add new flags."; >> default_call with >> args = []; optargs = [ OFlags ("flags", cmd_flags, Some []) ]; ret = RErr; >> permitted_states = [ Connected ]; >>+ modifies_fd = true; >> shortdesc = "send flush command to the NBD server"; >> longdesc = "\ >> Issue the flush command to the NBD server. The function should >>@@ -2625,6 +2649,7 @@ protocol extensions)." >> optargs = [ OFlags ("flags", cmd_flags, Some ["FUA"]) ]; >> ret = RErr; >> permitted_states = [ Connected ]; >>+ modifies_fd = true; >> shortdesc = "send trim command to the NBD server"; >> longdesc = "\ >> Issue a trim command to the NBD server, which if supported >>@@ -2656,6 +2681,7 @@ L<nbd_can_fua(3)>)." >> optargs = [ OFlags ("flags", cmd_flags, Some []) ]; >> ret = RErr; >> permitted_states = [ Connected ]; >>+ modifies_fd = true; >> shortdesc = "send cache (prefetch) command to the NBD server"; >> longdesc = "\ >> Issue the cache (prefetch) command to the NBD server, which >>@@ -2685,6 +2711,7 @@ protocol extensions)." >> Some ["FUA"; "NO_HOLE"; "FAST_ZERO"]) ]; >> ret = RErr; >> permitted_states = [ Connected ]; >>+ modifies_fd = true; >> shortdesc = "send write zeroes command to the NBD server"; >> longdesc = "\ >> Issue a write zeroes command to the NBD server, which if supported >>@@ -2723,6 +2750,7 @@ cannot do this, see L<nbd_can_fast_zero(3)>)." >> optargs = [ OFlags ("flags", cmd_flags, Some ["REQ_ONE"]) ]; >> ret = RErr; >> permitted_states = [ Connected ]; >>+ modifies_fd = true; >> shortdesc = "send block status command to the NBD server"; >> longdesc = "\ >> Issue the block status command to the NBD server. If >>@@ -2789,6 +2817,7 @@ validate that the server obeyed the flag." >> "poll", { >> default_call with >> args = [ Int "timeout" ]; ret = RInt; >>+ modifies_fd = true; >> shortdesc = "poll the handle once"; >> longdesc = "\ >> This is a simple implementation of L<poll(2)> which is used >>@@ -2810,6 +2839,7 @@ intended as something you would use."; >> "poll2", { >> default_call with >> args = [Fd "fd"; Int "timeout" ]; ret = RInt; >>+ modifies_fd = true; >> shortdesc = "poll the handle once, with fd"; >> longdesc = "\ >> This is the same as L<nbd_poll(3)>, but an additional >>@@ -3493,6 +3523,7 @@ and invalidate the need to write more commands. >> "aio_notify_read", { >> default_call with >> args = []; ret = RErr; >>+ modifies_fd = true; >> shortdesc = "notify that the connection is readable"; >> longdesc = "\ >> Send notification to the state machine that the connection >>@@ -3504,6 +3535,7 @@ connection is readable."; >> "aio_notify_write", { >> default_call with >> args = []; ret = RErr; >>+ modifies_fd = true; >> shortdesc = "notify that the connection is writable"; >> longdesc = "\ >> Send notification to the state machine that the connection >>diff --git a/generator/API.mli b/generator/API.mli >>index ff85849..4bf4468 100644 >>--- a/generator/API.mli >>+++ b/generator/API.mli >>@@ -41,6 +41,13 @@ type call = { >> if the function is asynchronous and in that case how one can check if >> it has completed. *) >> async_kind : async_kind option; >>+ (** A flag telling if the call may do something with the file descriptor. >>+ Some bindings needs exclusive access to the file descriptor and can not >>+ allow the user to call [aio_notify_read] or [aio_notify_write], neither >>+ directly nor indirectly from another call. So all calls that might trigger >>+ any of these functions to be called, including all synchronous commands >>+ like [pread] or [connect], should set this to [true]. *) >>+ modifies_fd : bool; >> (** The first stable version that the symbol appeared in, for >> example (1, 2) if the symbol was added in development cycle >> 1.1.x and thus the first stable version was 1.2. This is >>-- >>2.41.0